Joseph m



May 10, 1932. J, M, FFEY' 1,857,586

COMPOSITE INSULATING MATERIAL Filed Oct. 12, 1929 INVENTOR Jugahm'aftjey',

Y fl w, JMMZ/ ATTORNEYS Patented May 10, 1932 UNITED TATE JOSEPH .MI. GOFFEY, 01E SCHENECTADY, NEW YGTEK, ASSl'GiNtlZl-L lQ MEGA FHCJ'QULEEQER COMPANY, OF NEW YORK, IN. 3 A CQREOlt-ATIQN fil KNEW/l7 annsnrr COMIE'GSITE INSULATING BKATEREJ'LL Application filed October 12, 1929.

- My invention relates to a new composite material suitable for use as an electrical insulator and to a process for manufacturing the same. value where an insulator having both me chanical strength and high surface insulating pro erties is desired.

eretofore mica plate, thatis sheets composed of layers of mica flakes cemented together with a suitable binder and then pressed, have been'employed as insulators when high surface insulation was desired. Where mechanical strength was necessary due to the use of the insulator under strain, it was necessary to use plate of considerable thickness which substantially added to the cost of production; mica plate being a relatively expensive material. Furthermore, such insulators composed of thick mica plate had the disadvantages of not readily conforming to the irregularities of the surfaces between which the insulator was to be used. I have found that an insulator composed partly of asbestos and partly of mica or mica plate if suitably prepared possesses all of the advantages o'f mica plate used alone, while being more suitable for some purposes than the mica plate and being also more economical to produce. A suitable insulator may be composed of two mica plates, each composed of several layers of mica flakes and a sheet or sheets of asbestos between the plates, or of but one plate of mica with asbestos cemented toone surface thereof. When high surface insulation is desired at both surfaces of the insulator, then the construction using two mica plates with asbestos between is preferred, whereas if it is important for only one of the surfaces to have high surface insulation, mica on one side only of the asbestos is suflicient. A single layer of mica flakes ce mented to one or both surfaces of the asbestos may give sufliciently good surface insulation for some purposes.

In constructing the composite mica and asbestos insulator, preferably what is known as electrical asbestos, that is high grade I asbestos substantially free from conducting material is impregnated with a suitable binder such as shellac orglyptal. The 1m lhe invention is of particular Serial No. 899,368.

pregnated asbestos is then combined with uncured mica plate of the desired num r of layers, and the asbestos and mica plate are then cured and ressed together. The composlte plate is t en cut and moulded, pref- 555, erably in a cold die; the binding material being first softened by heat. If desired the asbestos and mica may be cured separately, in which case the asbestos should be pressed dur ng the curing. A satisfactory como poslte insulator may be made by using uncured asbestos having a thickness three times that of the uncured mica plate and the whole pressed to give the completed product the thickness of the original uncured asbestos. en

The composite insulating material is of particular value for commutator clamping rings where mechanical strength is needed and where engagement with the commutator requires high surface insulation of the ring. 7 The asbestos gives to the material a certain resiliency which causes the ring to conform more readily to irre ularities in shape of the commutator copper arsand thus permits a tighter commutator than would a ring conas structed of mica plate alone.

For a better understanding of the invention reference may be had to the accompany-- ingrdrawings of which:

i igure 1 is a diagrammatic mctional view so of a commutator clamping ring made from composite material built of asbestos and one mica plate;

Fig. 2 is a diagrammatic sectional view of a commutator ring built from asbestos and as two plates of mica;

Fig. 3 illustrates a step in the process of forming the commutator ring of Fig. 1; and

Fig. 4; is a perspective view of the ring of Fig. l.

lln forming a ring such as illustrated in Figs. 1 and 4 a disk 1 (see Fig. 3) of electrical asbestos, impregnated with shellac, and a disk 2 of uncured mica plate composed of mica flakes cemented together preferably at with glyptal and of a thickness less than that of the asbestos are placed one upon the other and then pressed and cured together between steam platens. The material while still hot from the presses, may be placed in a 20 faces are of mica; it being cheaper to proing the article in cold dies.

cold die where. it is cut and moulded into the has a more uniform thickness, and is conform illustrated in Fig. 1, viz: with the mica siderably cheaper to produce.

on the outer surface. If allowed to cool I claim:

after pressing, the material is reheated to 1. A commutator ring having its outer sur- 5 soften the cement before insertion into the face of mica plate prepared bycementing die. A similar method may be followed for mica flakes together with glyptal, said ring forming the ring illustrated in Fig. 2 using, having its inner surface of asbestos impregof course, two mica plates instead of. but nated with shellac. one. v 2. The method of preparing a composite m n The outer surface of the commutator ring insulating material of asbestos and mica is that which is in contact with the copper which consistes in first impregnating asbesbars when the ring is in position. It is imtos with a suitable cement, then combining portant therefore that there be high surit with uncured mica plate and finally pressface insulation along this outer surface of ing, curing and molding the same.

the ring, while such good insulation is not 3. The method of manufacturing an artiso essential for the inner surface. The ring cle for use as an insulator which consists in illustrated in Fig. 1 where mica forms the curing and pressing together asbestos imouter surface only of the ring, is thus prepregnated with shellac and mica flakes ceferred over that of Fig. 2 where both surment-ed into plates by glyptal, and then form- 1 4. The method of manufacturing an arti- Preferably when commercially manufaccle for use as an insulator which consists in turing a quantity of rings, the composite macuring and pressing together uncured mica terial is made in sheet form from large sheets plate and a resilient, heat-resistant material 5 of asbestos and mica plate rather than from impregnated with a cement having the charpreliminaril cut disks thereof as illustrated v acterlstics common to shellac and glyptal and for the pro uction of a single ring. then forming the article in cold dies.

Instead of using shellac for theimpregna- In testimony whereof, I have signed my tion of the asbestos and glyptal in preparing name to thls speclfication.

so the mica plate, either shellac or glyptal could JOSEPH M. COFFEY.

be used for both purposes. G yptal is superior to shellac when used in electrical insulators, but is more costly. The use of glyptal with the mica and shellac with the asbestos as suggested above combines the ad- 10 vantages of glyptal where needed, namely in contact with the copper bars, with the cheapness of shellac where the electrical properties of glyptal are not necessary. Both shellac 40 and glyptal are binders which are characterized by the fact that they are curable to a controllable degree, may be afterwards softened at temperatures around 300 F. sufliciently to permit of molding of the material impregnated therewith and may again be softened no when the material is in use sufficiently to permit the material to conform to irregularities of the engaging surfaces. Any binders having similar characteristics to shellac and glyptal are suitable for use in preparing the composite asbestos and mica insulating material. In place of the asbestos it is possible that other resilient heat resistant materials might be substituted therefor. Asbestos is preferred, however, both on .account of its high heat resistant properties and because it has no tendency to carbonize in the event of w an electrical discharge on its surface. 60 A composite insulator as compared with one composed only of mica plate is stronger for the same thickness, conforms more readily to surface irregularities, has as high surface insulation on its mica surface, cau ses 65 less wear on the dies during manufacture, 

